1. Field of the Invention
This invention relates to feed tables used for clamping and feeding elongated workpieces to a machine tool, such as a band saw, and more particularly, to a feed table with a force reaction system for counteracting the deflection in a shuttle vise normally caused by clamping the workpiece.
2. Description of the Prior Art
On machine tools, such as band saws, used for cutting elongated bar stock or other types of workpieces, devices, generally called feed tables, have been developed to clamp the workpiece and feed it toward the machine tool. In some prior art feed tables, a movable shuttle vise is used to clamp the material and then move it along a conveyor to a desired point at which the material is to be cut. The process is repeated as often as necessary until the workpiece is fully utilized. The feed tables are frequently automated. The feed table includes a roller conveyor assembly which provides rolling support of the workpiece. In one prior art device, a fixed vise assembly and the movable shuttle vise assembly are attached to a frame on the feed table. The fixed vise and shuttle vise assemblies cooperate to grip and stabilize the workpiece during cutting by the machine tool in addition to the shuttle vise being adapted to move the workpiece toward the cutting area of the machine tool.
When production cutting on bar stock is performed, the feeding and cutting sequence typically includes a series of automated steps such as: gripping of the workpiece with the movable shuttle vise assembly, releasing the fixed vise assembly, advancing the workpiece toward the cutting area of the machine tool by moving the shuttle vise assembly along the conveyor, stabilizing the workpiece by clamping it again in the fixed vise assembly, cutting the workpiece as desired, releasing the movable shuttle vise assembly and moving it away from the cutting area while continuing to clamp the workpiece by the fixed vise assembly, gripping the workpiece again with the movable vise assembly, releasing the fixed vise assembly, and again advancing the workpiece toward the cutting area of the machine tool for the next machining operation. This series of steps is repeated as desired.
Feed table designs such as these generally include opposing vise jaws cantilevered upwardly from vise bases which are fixedly mounted in the case of the fixed vise assembly, or movably mounted on feed table guide ways in the case of the shuttle vise assembly. These upwardly cantilevered jaws have been found to have a common problem, namely, when clamping workpieces, and in particularly large workpieces, the opposing jaws tend to spread out or open up at the upper portion of the jaws. As the jaws are pushed against the workpiece by an actuating mechanism such as a hydraulic cylinder, the resistance to compression exerted by the workpiece causes the upper portions of the jaws to separate outwardly.
Such separation can be problematic because the workpiece will not be properly gripped by either the fixed vise assembly or the shuttle vise assembly, and this may permit the workpiece to move or slip upwardly and/or axially before or during the cutting sequence. If this occurs, the workpiece may not be properly cut which adversely affects cutting precision and accuracy, and in extreme situations, necessitates scrapping the workpiece or portions cut from it. Examples of such feed tables are disclosed in U.S. Pat. Nos. 4,179,961 and 3,504,585 to Harris and U.S. Pat. No. 3,474,693 to Wilkie, et al.
As the length, diameter, and accordingly the weight, of workpieces increase, machine tool feed table conveyors have employed guide roller assemblies which include a plurality of side-by-side rollers capable of supporting and advancing larger and heavier workpieces. Some prior art feed tables also have included reaction frame assemblies which add substantial lateral stability and rigidity to the opposing jaws of the fixed vise and/or shuttle vise assemblies. One such prior art feed table is disclosed as prior art in U.S. Pat. No. 5,353,910 to Harris. This prior art device includes a vise reaction frame assembly which extends over and under the guide roller assembly. The vise reaction frame assembly is positioned to resist the tendency of the opposing jaws of the shuttle vise assembly to open up in reaction to clamping the workpiece. The shuttle vise assembly includes at least one movable jaw mounted to a first upright post and another jaw mounted to a second upright post and which may be rigidly affixed thereto. The reaction frame assembly includes cross beams which are rigidly secured between the top and bottom of the first and second posts and thus encircle the guide roller assembly. Accordingly, gripping of a workpiece with a vise having such a reaction frame is very positive because the previously described reaction forces are resisted by the reaction frame assembly. This reduces the tendency of the opposing jaws to spread apart during clamping of the workpiece.
In order to provide for movement of a shuttle vise assembly having such a reaction frame, the shuttle vise assembly must be capable of moving longitudinally along the guide roller assembly. Thus, the lower cross beam may be mounted on a pair of drive screws which reciprocate the shuttle vise assembly relative to the roller assembly. In operation, the drive screws cause the shuttle vise assembly and the vise jaws mounted thereon to move along the feed table outside longitudinal roller frame members which support the rollers in the guide roller assembly. Other types of guide rail systems could also be used. However, this construction requires that the guide roller assembly be raised and mounted on support legs at the ends of the roller frame members so that the cross beams can pass above and below the roller frame members. This prior art invention disclosed in U.S. Pat. No. 5,353,910 to Harris will be further discussed herein.
Accordingly, although such reaction frame assemblies effectively counteract the reaction forces caused by clamping the workpiece with the vise jaw, they require a long unsupported span of roller frame members between the support legs. This span requires that the roller frame members be sized significantly large enough to provide strength for the entire roller frame assembly when supporting the workpiece. This greatly adds to the bulk of the roller frame assembly and still may not be sufficient to prevent undesired movement or deflection thereof when handling very large workpieces. There is a need, therefore, for a feed table with a force reaction system which can counteract the clamping forces to avoid deflection of the jaws but which allows the roller frame assembly to be mounted directly onto the feed table for greater support and to eliminate the lower cross beam.
The present invention solves these problems by providing a feed table with force reaction system which counteracts the deflection of vise jaws caused by actuation thereof by applying substantially equal forces to the vise in opposite directions from the clamping forces.